Shaft positioning apparatus



Jall- 2, R W. MAY

SHAFT PSITIONING APPARATUS Filed June '7, 1946 4 Sheets-Sheet 1 w w w,

Jan. 2, 1951 Filed June 7, 1946 R. W. MAY

SHAFT POSITIONING APPARATUS 4 Sheets-Sheet 2 Jan. z, 1951 R. WIMAY2,536,070

SHAFT POSITIONING APPARATUS Filed June 7, 1946 4 Sheets-Sheet 5 Jan, 2,1951 R, W, MAY 2,536,070

' SHAFT POSITINING APPARATUS Filed June 7, 1946 I 4 Sheets-Sheet 4 QH l74 U 503mm ZEW/@17021 Patented Jan. 2, 1,951

SHAFT POSITIONING APPARATUS Richard W. May, Cedar Rapids, Iowa, assgnorto Collins Radio Company, a corporation of Iowa Original applicationDecember 22, 1943, Serial No. 515,250. Divided and this application June7, 1946, Serial No. 674,984 i 5 claims. (o1. 'i4-10.2)

This invention relates to shaft positioning apparatus, and moreparticularly to improvements in apparatus especially designed forautomatic tuning of radio equipment.

One feature of this invention is that it provides` means fordisconnecting the tuned shaft` from the automatic drive means whenadjustments are being made of the stop members mounted on the shaft;another feature of this invention is that it enables new tuningpositions to be set up or se-` lected with great ease; still anotherfeature of this invention is the provision of a new drive arrangementfor the selecting means; yet another feature is that the selectingmeans, and more particularly the selector switch, operates for only abrief period of each tuning cycle of operation of the mechanismyafurther feature of `thisinvention is that the selector switch may bearranged in a separate unitfrom theremainderof the` tuning apparatus;still a further feature of this invention is the provision ofcooperating stop ring and pawl surfaces arranged with an angle ofcooperation such that the pawl will hold the stop ring in positionduring set-up operations, `but will be automatically forced up out oftheslot `upon initiation of an automatic tuning operation;

and yet a further feature of this invention is the use of a curved stopsurface on the portion of the stop element cooperating with the stopring.

Other `features and advantages of this invention will be apparent fromthe following specication and the drawings, in which: i i

Figure 1 is a side elevational View of positioning apparatus embodyingthis invention; Figure 2 is a transverse sectional view along `the line2-2 of Figure 1; Figure 3 is` a partial sectional view along the line3--3 of Figure l; Figure 4 is a view along the line 4--4 of Figure 5gFigure 5 is a transverse sectional view along the line 5-5 of Figure 4;Figure 6 is a fragmentary sectional View along the line 6--6 of Figure4; Figure 7 is a front elevational view of an operative combinationcomprising a limit switch, a tuning unit, and a selector switch; Figure8 is an enlarged detail View,

partly in section, of the limit switch; Figure 9 is.

side elevational view of the selector switch; Fig-` .ure 13 is asectional `view of the selector switch,

along the line |3-I3 of Figure 12; and Figure 14 t is a circuit diagram.

This application is a division er my Patent No.

12,512,644 The improvements to which the pres-` ent application isprincipally directed comprise an improved shape of the stop ring slotand the cooperating pawl end. l

The apparatus illustrated and `described here contains improvements inautomatic tuning devices of the kind shown in various patents heretoforeissued to Arthur A. Collins, as for example Collins Patent No.2,285,414, which issued June 9, 1942; and in various copendingapplications of `the said Arthur A. Collins and of myself. In `automatictuning devices of this type the tuning element shaft is connected to adrum on which are rotatably mounted a plurality of stop rings havingstop shoulders adapted to cooperate with stop elements or pawls. Thereare a similar number of `pawls and stop rings, each combinationproviding a stop assembly adapted to automat- `ioally stop the shaft atany predetermined position by engagement of the stop shoulder with thecooperating pawl.

In operation, a drive motor, through appropriate intermediateconnections usually incorporating a line shaft, rotates the stop ringdrum in one direction until the drum has reached a terminal positionwhere it stops, the drive then `continuing operation further (slipping aclutch provided for this purpose) until a selector cam drum and aselector switch reach a position determined by the electrical circuitselected. There-upon the drive motor reverses and the drum and tuning`shaft are driven in the other direction until the operative pawl(selected by the position in which the selector cam drum stopped)engages the stop shoulder of its cooperating ring, whereupon the tuningshaft is stopped at the desired preselectedposition. The drive motor anddriving `con- V nections again continue rotation further (throughtheaction of the slip-clutch) until the cycle of operation is terminatedby a limit switch.`

In operation the stop rings must, of course, be ixedly mounted indesired position on the stop ring drum, and means must be provided forlocking them in such position. `When it is desiredto `change theselection of frequencies to which the radio equipment is automaticallytunable, the stop. rings must be released and permitted` rotationalmovement on the drum to enable setting up or selection of the newstopping `positions of the shaft. A novel means for effecting thedesired locking and unlocking, and for operating the locking means fromthe front of the dial, has recently been devised by said Arthur A.Collins and is `claimed in his application Serial No.

472,717, tiled January 18, 1943, this loclringlmeans Lbeing shown in theapparatus illustrated here.` f

When the locking means has been unlocked or released and the stop ringsare movable on the shaft, a new position is selected by rotation of theshaft, the stop ring being held in place during such rotation bycooperation with its associated pawl, the stop combinations beingrendered operative and adjusted to a new position, when desired, one ata time. Since the power-operated drive means is stationary during thisset-up operation, the shaft could be manually turned only by overcomingthe resistance of the slip-clutch,

and causing it to slip, in the absence of means for disconnecting thedrive. Where the automatic tuning apparatus is designed for heavy" dutyuse, the slip-clutch must provide considerable driving torqueand thisrenders it diiiicull to manually rotate the shaft during set-upoperations. Accordingly, I have devised an arrangement whereby releasingof the locking means simultaneously disconnects the shaft from the..automatic or power operated drive means, so

that the tuning shaft may be freely and easily rotated manually duringset-up operations.

In automatic tuning apparatus heretofore recently used, and shown indetail in the above mentioned Collins application 472,717, the cam drumand selector switch are caused to start rotating immediately uponinitiation of a tuning cycle, the selector cam positively withdrawingthe pawl from its cooperating slot in the stop ring. This requiresconsiderable rotation of the selector switch, many times more turns ofrotation than would otherwise be necessary, with resultant undue wear onsuch switch. I have devised and am here disclosing and claiming anarrangement whereby the pawls and stop rings retain their desiredassociation during set-up operations, yet are automatically disengagedby reasonI of rotation of the tuning shaft upon initiation of a tuningcycle; and having provided an Yimproved drive arrangement for theselector means, and more particularly the-selector cam and selectorswitch, such that neither of these elements operates until the tuningshaft has reached its terminal or home position, whereupon the selectorelements operate briey to effect the desired selection, and then remainstationary during the remainder or tuning portion of the cycle ofoperation.

Inasmuch as the construction and general operation of automatic tuningapparatus analogous to that illustrated here has been described inconsiderable detail in the aforementioned Collins Patent 2,285,414, andin other copending applications directed to other features, it will bedescribed more briefly here. In so far as the general operation and usesof such apparatus are concerned, the present specification is intendedto provide only sufficient detail to enable understanding thereof, sincereference may be had to the above-mentioned patents or to otherpreviously issued Colins patents on automatic tuning devices for a morefull description of such general operation; but the novel features towhich this application is particularly directed will be described Withmore detail.

Figure 7 illustrates an operative combination for automaticallypositioning a tuning shaft at any desired point within a singlerevolution, this comprising as its principal parts a main operatingortuning unit here identified as A and supplemental units forming part ofthe means for Selecting the stop combination to be operative in the mainunit, these here being shown as comprising a limit switch unit B and aselector switch unit C. The selector switch unit may also be used foreffecting changes in the circuit condition, if desired, since it assumesdifferent positions always related to one of the preselected positionsto which the main tuning shaft will be positioned by the operating unitA. For example, switching of crystals for different transmissionfrequencies may be effected by a switch connected to the shaft of theselector switch C. Its principal function, however, is concerned withselection of the desired stop combination in the main tuning unit. Allof these units are driven from a single drive means, which may comprisea reversible electric motor operative through a line shaft hereidentified as D. The details of the construct-ionV of the main operatingunit A are shown-in; Figures 1-6; the limit switch B is shown in moredetail in Figures 8-11; the selector switch and its drive are furthershown in Figures 12 and 13; and Figure 14 is a diagram of an operativecircuit for the system.

Referring now more particularly toV Figures 1-6, it will be seen. thatthe parts cooperatingto effect automatic positioning of the shaftk of1 acondenser or other tuning element, asthe shaft lil, are arrangedv in aself-contained unit mount'- ed between the endV plates ii and l2 held inappropriate relationship by the posts i3. A drum lil is fixedly mountedon; the shaft IB; this drum having a longitudinally but non-rotatably.-movable forward portion idc adapted'. to be moved longitudinally of theshaft bymeansoperative by a manually rotatable bar- I5 onthey face-ofthe tuning dial IG. The drum carries anydesirednumber (here shown as l2)of tuning stop rings, these being here identified asv iTaf-ZiAppropriate non-rotatable spacer. washersare provided between these stoprings, both the rings and washers being axially. movable onthe-drum.When the end portion lila. of the drumvis moved to the right (speakingwith respecttothe-position of the parts as shown in Figure e) the stoprings are loosened and.y unlocked and' may be individually set todesired positions.; and when the end portion Ida of the drum Virs-movedtothe left, with considerable force, the stop rings are locked orclamped in theselected positions.

A'. plurality of tuning positioning pawls or stop elements Ilia-Z areprovided, the shape-andllocationof these pawls being best seen fromconsideration of the pawl itc shownr in Figure 2. Each pawl has itsoperating endurged" toward the cooperating stop ring by one ofay similarnumber of springs it. When a pawl is rendered operative by the selectingmechanism, its end moves in toward the stoprings and: ridesupon thesurface of the cooperating stop'ring untilfthe slot therein is reached,whereupon the pawl-end drops into the slot and stopsthering (andl thusthe tuning element shaft lle), as may be-best seen in Figure 2. Stoppingofrthestop ring drum- |4 in either of its two terminal-positions,approximately-.3609 apart, is effected by cooperation Vbetween aterminal stop paWlfZi'Jand-an appropriate lug portion on a terminal stopring 2|, this ring being keyedto the drum.

Rotation of the stop ring drum is eected; by a drive motor and lineshaft; asprevicusly mentioned, having driving connection with the gear212 asv through the worin 22a shown in Figure As may be bestY seen inFiguree, the gear 22:v is mounted coaxially with the shaft iii;A but' itis freely rotatable about suchshaft. Itis rigidly connected to a gear 23which drives thegear. 2,4, thedri'vingelement of a lostmotion connectionhaving a driven element 25, these two elements being spaced but coaxial.i This driven element is connected to and rotates the selector cam drumcarrying a plurality of selector cams 26a-J. These cams are 12 innumber, and have depressions in their periphery, the arrangement beingsuch that the depressions are equally `spaced about the periphery of thedrum (as may be best seen in Figure i), so that they `form a helixtherearound. The selector cam drum is rigidly mounted on a shaft `2tpinned to the driven element 25 and serving as a bearing member for thedriving element 2li.

In operating the device to automatically select a new tuning position,the operator selects a certain circuit by a manually rotatable switch orother type of switch, as a telephone-type dial switch. A motor relaystarts the drive motor and drives the gear 22 in a direction such as to`rotate the main shaft and stop ring drum counter-clockwise (as viewedin Figure 2) until the yshaft is stopped in terminal or home position bycooperation of the terminal stop ring 2i and terminal stop pawl 2t. Thedrive then continues further, rotating the selector cam drum andselector switch, unt-i1 the open-circuit portion of the rotatablemember' of the selector switch reaches the contact or tap correspondingto the selected circuit, whereupon the motor relay holding circuit isopened and `relay operation causes the drive motor to reverse. The driveis then in Such a direction that` the stop ring rotation is clockwise(as viewed in Figure 2), the `selector cam drum being ieft standing atthe selected position by operation of the lost motion drivingconnection. When the stop ring reaches the position shown in Figure 2the `pawl end drops into place in the stop ring slot and the tuningelement shaft IG is positively stopped by engagement of the stopshoulder with the stop element (speaking with respect to the parts ofthe stop combination selected by the selector cam), the motor thencontinuing operation ofthe drive means until a limit switch finallyterminates the cycle.

In order to enable this over-running action `of `thedrive at both ends`of the movement of the stop ring drum, a slip-clutch is provided in the"driving connection between the gear 22 and the shaft Iii. As maybe bestseeen by an examina- 'tion of Figure 4, the clutch includes a cup-likemember 33, comprising a cylindrical drum portion 33a and an inwardlyextending end portion 33h. Within the drum portion. are a plurality offriction shoe units here identified as 33e-f, these friction shoeshaving their ends normally urged apart, so as to expand them intofrictional engagement with the drum 33a, by springs ed on the shaft IIJand rigidly `connected to the gear 22.

, As may7 be bestseen in Figure 5, rotation of the gear exerts a drivingforce on one or the other end of the friction shoes; and this force istransmitted frictionallyfrom the` outer surface of the shoes 33e-Ito thedrum 33a. The force transmitting arrangement is such that rotation ofthe gear tends to pull the ends of the shoe in away from the drum, thisresulting in a more uniform slip point or maximum torque. The slipclutchoperates, of course, as a torque limiting `,a1rangement; and it isdesigned to transmit any mum torque .isexceedea f Referring now moreparticularly to Figure 4, it will be seen that the stop rings I1 arerotatable on the drum le, while the intermediate spacing washers arekeyed to this drum by portions lying in the slot ilib. rIhe locking bart5 comprises the actuating end of a stud having the shaft portion 35threaded into an opening in the end of the shaft It. The inner end ofthethreaded shaft 35 is received ina recess in and bears against a pressuremember 35 slidably but non-rotatably movable with respect to the shafti0, this member bearing against the movable mem-ber Ilia of the stopring drum. It will be apparent that rotation of the locking bar I5 in adirection screwing the stud into the shaft iB (preferably clockwise)forces the end Ida of the drum to the left (speaking with respect `tothe position of the parts in Figure 4) and clamps the stop `ringsagainst the flange Hic at the left-hand end of the stop ring drum, the`friction between the stop rings and the spacing washers locking `thestop rings immovably in place when the locking arrangement is drawn uptight.

When it is desired to change the-positionfoi one or more of the rings,it is only necessary/pto back thelocking bar off slightly in unlocking`direction` (merely a half turn or so) #whereupon the clamping pressureis sufficiently released` to enable the rings to be changed to newpositions, This is readily done by actuating the automatic tuningmechanism `so that `the device goes through its automatic tuningcycleand leaves the particular stop combination which it is desired tore-set (or initially set up) in the position shown in Figure 2. It isthenonly necessary to loosen the locking bary and manually rotate theshaft le by use of the dial IS, this resulting in rotating `the shaftwithout rotating the stop ring, held in positionby its cooperating pawl,so thatithere is relative movement between the shaft and the stop ring.If the dial is held `in the desired position( tightening the lockingmeans again by rotation of the locking bar results in selection ordetermination of `a new tuning position for the particular stopcombination thus adjusted. i i

Since the drive arrangement connected to the gear 2'2 `is immovableduring this manual rotation of the shaft I, I have found that it ispreferable to provide means for disconnecting the shaft from the`power-operated drive arrangement during setting up or `adjusting of theposi,- tions of the stop rings.` I accomplish this ina very satisfactoryand effective method by providing what is in effect another connectingclutch associated with the slip-clutch 33, and actuated byand inaccordance with operation of thestop ring locking means.` As may be bestseen `in Figure `4, the cup-like element of the slip-clutch has its endportion 3th lying between theY back iiange I ic of the stop ring drumand the first ,stop ring at this end, here identified as 2i., Op-

On` the other hand, releasing of the stop ring locking means alsoreleases or unclamps the portion 33h, so that the shaft IU and stop ringdrum are freely rotatable with respect -to the cuplike member when thelocking arrangement is in released` position. This provides a compactand simple connecting and disconnecting, ar-

rangement which uses thecup-like memberboth as thedrum element of theslip-clutcnanduas aseaovfo ne ofthe elements of a friction or connectingclutch.v This disconnecting feature is particularly desirable inconnection with heavy duty equipment, where manual force running up in-Ailafon the line shaft D, makes lost motion connection with a drum 4l,this connection being through'engagement of a pin or itc with a pin Mamounted in the drum di. A friction shoe 42`encircles the drum l and isin frictional engagement therewith, the lower ends of this shoe beingpulled together, as may be best seen in Figure 8, by a spring 42C. Whenthe line shaft has just rotated in such a direction as-to causeengagement between the pin lz'b and Ma (as shown in Figures l and 1.1),the limit switch would stand in the position shown in Figure 8. On theother hand, when the cycle of operation is nearing its end, the pin decomes around into engagement with the pin da, resultingin clockwiserotationof the drum d! (as viewed in Figure 8) whereupon the end da orthe friction shoe 42 moves the operating element i3 of the limit switch,operating with a snap action (through the spring 43a) to throw themovable contact 44 out of engagement with the contact and intoengagement with the Contact Ll'. This terminates one cycle of operation.and leaves the system in condition for the next cycle.

Referring now more particularly to Figures 12 and 13, the selectorswitch C ifs-shown as comprising a plurality of taps or contacts' 50a-Zequally spaced' around a central rotatable member 5I, this member havinga slotror open circuit portionhere identified as 5in and shown adjacentthe contact 58e. The movable contacts are mounted on a member rigidlyconnected to and' carriedby an adjustable member 52, this member beingmcyablewith respect to the main frame of the selector switch andadjustable-to a desired position, therproper positionloeingmain-tainedby tightening-down-a stud 53 extending through a slot inthe-member- 52, as may behest seen in Figure The.V rotatable member Elis carried on and drivenhy` a shaft 54, this shaft being rigidlyconnected tothe ure` 4. Intermediate'the driving and-'driven ele-`1nents 2t and 2.5' arefapluralityvof eared washers 21m-f;and-intermediate the driving andi driven elements Edf-and 5'! are aplurality of similar eared washers 5ta-f. The first of such washers ifsin each-case fastened to the driving element and the last of'suchseriesl oi washersY is-connected tothe driven element; andtheintermediate washers are Vfreelfy'- rotatable, the washers-all :beingseparatedby spacers. The Washers f illustrated are provided with ears orlugs'on opposite sides apart),- and bent in the: opposite directions.When the Washers are allin the position shown in Figure l2, for example,rotation of the' driving element55 and the washer 56 can take place fornearly a turn without rotation of any other element; but then the ear'ofthe washer 56a shown at the bottom in Figure 12 comes in contact (afterits rotation for approximately a turn) with the oppositely bent earshownat the top of the next Washer 56h, and thereupon such washer startsto move. These two washers then move for nearly a turn before the nextwasher 55C starts to turn, and soon until iinally the driven element-isrotated. This enables the driving element to make more. than 'onecomplete revolution, generally two or three revolutions in practice,Without rotation of the driven element.

In operation of the automatic tuning system, reversal of the motor foroperation of the drive means in the tuning direction backs off the-lostmotion connections, without movement of the selector switch or stop ringdrum, until the'Y cycle of operation has been completed it beingnecessary that the lost motion connections have sufficient lost motionfor this purpose'. When the next cycle of operation is initiated, thedrive means rotates in the other or homingV direction without initialmovement of the selector switch or selector cams, merely taking up theslack in the lost motion drive until the shaft has reached home positionand the clutch has started to slip. When the drive means hasv operatedlongenough to have rotated the shaft through one complete revolution,all of the slack is taken out of the lost motion driving. connection andthe selector switch and cam drum start to rotate, this rotation being insynchronism because of the similarity of the-two lost motionconnections. Such selecting rotation continues until the movable member5| reaches a position where its slot is adjacent the energized contact,as the contact ilc, whereupon the drive means reverses and the timingYportion-of the cycle-takes place. the selector switch and selector camremaining unmoved during this portion of the operation by virtue ofthelost motion driving connections. This arrangement enables theselector switch and selector cam drums to` be in separate units, ifdesired, it only being, necessary that the lost motion connections besimilar in operation; and results in the selector switch rotating lessthan one full revolution in each tuning cycle, since it r does not startto rotateuntil the system is ready for the selecting operation.

Inasmuch as the selector cam drum does not start'rotating immediatelyupon initiation of a tuning cycle, it cannot be used to withdraw thepawl from the slot of the Stop ring with which it cooperated on theprevious tuning cycle. In order to solve the problem thus4 presented, Ihave devised an improved shape of the stop ring` slot and thecooperating end of the pawl. Referring more particularly to Figure 2, itwill be seen that the pawls i8 are all carried by' and rotatable on apawl shaft here identied as 18m. In order to facilitate entry of thepawl into the slot in the stop ring, and to ensure the samepositioningof theY shaft even if Athe'- distances of entry' differ indifferent tuningcycles; I form the outer or stop end 18e of the pawl 18ewith a curvature having the axis of the shaftV` Im as its center; andhave this portion-cooperate with aradial stop shoulder', or stop edgellc' of the stopringi slots. The surfaces Hc and 18e' are the surfaceswhich come into engagement during the tuning operation and which stopthe shaft at the selected position, and it is for that reason that theseare termed the stop surfaces. On the other hand, when a new tuning cycleis initiated, the stop ring Hc rotates in a counter-clockwise direction(speaking with respect to Figure 2) and the other surface llc must actupon the other edge lc" to withdraw the pawl or force it out ofthe slot,thesebeing termed the withdrawing surfaces. The width of the slot and ofthe end of the pawl are preferably so proportioned that the pawl cannever drop fully down to the bottom ofthe slot, but assumes a stoppingposition as shown in Figure 2. This ensures close engagement between thestopping surfaces on the one `hand and the withdrawing surface on theother hand; and enables adjusting of the tuning position, during set-upoperations, `by rotation of the shaft lll in either direction to thedesired position, without any lost motion.

In order toihave the pawl remain in the `slot and hold the stop ring llcstationary despite the small frictional drag on it occasioned byrotation of the shaft iti during set-up operations, the arrangement ofthe withdrawing surfaces mustibe such that withdrawal does nottake placeas a result of this relatively low force. On the other hand, when thestop rings are locked up` and automatic tuning operations are takingplace, the force resulting from the drive through the slipclutch 33 mustbe sufficient to result in withdrawal of the pawl of the previouslyenergized stop combination, so that a force within the torque limitationof the slip clutch must eifect withdrawal of the pawl. If the pawl andstop ring be considered as having no friction between the withdrawingsurfaces, the desired angle a made by the surface Ic with a radius ofthe stop ring to the point of contact may be found from the followingformula: i

C-A sin B A cos B c==arc tan used must be taken into considerationandthe correct formula for the angle between the with?- drawing surfaceof the pawl and the stop ring radius to the point of contact is asfollows:

C A sin B A cos B where is the friction angle. In the case of an actualembodiment of this invention which I have constructed, the tangentialforce at the peripha=arc tan ery of the stop ring was selected aspounds,

`the particular slip-clutch used providing conciderable margin of torqueover this tangential force; the springs used provided an inward. forceof .375 pound on the end of the pawl; the angle between a tangent at thepoint of contact and a line from the point of contact to the pawl shaftwas 11; and the withdrawing surfaces wereboth steel, resulting in afriction angle of 8.5 degrees. Calculation, by use of the formula lastset forth above, showed that the angle a should `have a value of +4.25(minus 4.25c plus 8.5)., Giving the withdrawing surface of the pawl thisangle with respect to the stop ring radius at the point of contact (asillustrated in thedrawings) resulted in sumcient holding force for allseteup operations and for proper adjustment ofthe stop rings on theshaft with movement of the shaft in either direction, together withimmediate and automatic withdrawal of the pawl uponinitiation of atuning operation, when the stop rings `were locked in place. That is,the pawl would stay in the slot when the torque at the periphery of thestop ring was less than 3.2 pounds, but would withdraw from` the slotwhen this force was ex,-

ceeded. r ,i

Referring now more particularly to -the circuit diagram, Figure 14, abattery is illustrated as representative of any appropriate source ofpower for the motor and relays. The motor control relay 6I has anactuating coil Gla, three movable switch members SIb-fd, three uppercontacts Ble-g, and two lower contacts @lh and Sli. This motor controlrelay and the limit switch B, in conjunction with the selector switcharrangement C, operate to achieve the desired electrica sequence ofoperations.` i i i A manual selector switch,.identiied in general as 62,is here shown as having l2 taps 62al wired tothe corresponding switchpoints 50a- Z of the automatic rotatable selector switch,` the manualswitch arm 62m being adapted to engage any one of the I2 switch pointsand thus to complete a circuit to any one of the corresponding automaticselector switch contacts. The localeremote switch 63 is shown `in aposition enabling control by the manual selector switch. A relay 54 hascooperating contacts 64a and 64b which form part of the control circuitof the tuning system, and other contacts 64e and 64d which control someother circuit condition, as carrier emission. This relay and the switch65 (which may be a key or a microphone button) provide an interlockedaction preventing operation of the set while the automatic tuningldevice is in operation, and vice versa.

Assuming that the parts are in thepostion shown in Figures 1-13 of thedrawing and it is desired to select another frequency setting, movementof the switch arm 62m might be made to the contact 62d, as shown indotted line position. This movement completes a circuit from groundthrough the rotatable element 5l of the selector switch, contact 5nd,wire t6, contact 62d, arm 52m, wire El, switch B3, contacts Eta and 64b(it being assumed that the switch 65 is open), wire 68, motor relay coilBla, wire 5S, battery BIJ, and wire 10 back to ground. This energizesthe motor control relay and causes its movable switch elements Elbe-d tomove from the position shown to Vtheir lower positions. This energizesthe reversible drve motor 1| by acircuit from the., ungrounded side ofthe battery through the wire 12. The eld lla of the motor is constantlyenergized; and in this relay position the armature is energized by acircuit including contacts Blc and 6 Iy, the wire 13 to the upper end ofthe armature, and a return circuit from the lower terminal of thearmature through the wire 14, the contacts G lb and Glh and the wire 10to the grounded side of the battery 6D. This effects rotationof themotor in the home direction, lifting the pawl I8c out of the slot in thecooperating stop ring. At the same time the limit switch member 42 opensthe circuitbetween the contacts 44 and 45, ensuring against operation ofthe set `untilthe tuning cycle is complete, and brings the movablecontact 44 into engagement with the contact'di. Whenthe shaft lhasreached home position the lost motion drive connections initiaterotation of the selector switch and selector cam. As soon as the switchmember I reaches a position such that its slot is opposite the contact50d, the motor control relay circuit is de-energized and the motor stopsand immediately reverses, movement of the parts in the other directionleaving the selector cams and selector switch stationary in positions`corresponding to the selector tap 50d.

' Deenergization of the motor relay coil 61a causes return of itsmovable contacts cib-d to the position shown in the drawing', completinganother circuit to the motor armature in such a way as to cause itsoperation in the opposite direction. This circuit leads from theungrounded side of the battery through the wire 72, the contacts 6|c and6H, the wire 15, the limit switch contacts 45 and 44, the Wire 16,contacts El?) and Gle. and the wire '[4 to the lower armature terminal;and from the upper armature terminal ,through the wire 13, the contactsGld and Gig, and the wire 'IT back to the grounded side of the battery,it being noted that the connections to the amature terminals are nowreversed with respect to the batttery. This causes movementof themechanical parts in the tuning directionythis continuing until thetuning shaft is stopped the selected stop combination, and continuingfurther (with the clutch 33 slipping) until the Vlimit switch 42 opensengagement between the Icontacts 44 and 46. A bridging resistor i8 vmaybe associated with these contacts to provide a small current keeping thepawl in firm engagement with the stop shoulder of its cooperating stopring, this force being insuicient to slip the slip-clutch 33.

While I have shown and described certain enibodiments of my invention`it is to be understood that it is capable of many modications, Changes,therefore, in the construction and arrangement may be made withoutdeparting from the spirit and scope of the invention as disclose in theappended claims.

I claim:

1. In apparatus for positioning a rotatable shaft having selector means,stop means of the character described, including: reversible,torquellimiting drive means adapted to rotate the shaft and adapted onlybriefly to operate the selector means; a stop ring movably mounted onsaid shaft and having a slot therein; locking means adapted ,selectivelyto prevent or permit rotation of said shaft with respect to the ring;and a pivotally mounted pawl lhaving an end portion 'adapted to bereceived by the slot to effect the desired stopping, the surface of thepawl end vopposite the stopping surface when the pawl is movement of theshaft with respect to the stop ring, but a force within the torquelimits of 'said drive.

y 2. VIn apparatus for positioning a rota-table shaft, stop means of thecharacter described, including: a stop ring mounted on said shaftandhaving a slot therein; means for locking saidringj nonrotatably on saidshaft during said position? ing operation; means for releasing .saidlocking `means to permit said ring to rotate with respect to said shaftwhen a frictional `drag is ex' ceded; and a pivotally mounted pawlhaving an end portion adapted to be received by the slot to effect thedesired stopping, the construction being such that withdrawal of the endportion of the pawl from the slot is effected by a rotational force inexcess of said frictional drag and of predetermined value exerted by theStop ring, but only when such force is at least as great as saidpredetermined value.

3. In apparatus for positioning a retable shaft, stop means of thevcharacter described, including: a stop ring mounted on said shaft andhavingr a radial slot therein; means for locking said ring nonrotatablyon said shaft .during said positioning operation; means for releasingsaid locking means to permit said ring to rotate .vith respect to saidshaft when a frictional drag exceeded; and a pivotaily mounted pawlhaving an end portion adapted to be r 'ved by the slot to eifect thedesired Stopp g, the stopping surface of the pawl end comprising an arcconcentric with the axis of the pivotal movement of the pawl, and thesurface of the pawl end opposite 'the stopping surface when the pawl isin stopping position making an angle of less than 10 with a radius ofthe stop ring through its point of contact therewith, withdrawal of theend portion of the pawl from the slot being effected by a rotationalforce in excess of said frictional drag and of predetermined valueexerted by the stop ring, but only when such force is at least as greatas said predetermined value.

d. In apparatus for positioning a rotatable shaft, stop means of thecharacter described, including: reversible, torque-limiting drive meansadapted to rotate the shaft; a stop ring mounted on said shaft andhaving a slot therein; means for locking said ring ncnrotatably on saidshaft during said positioning operation; means for releasing saidlocking means to permit said ring to rotate with respect to said shaftwhen a frictional drag is exceeded; and a .pivotally mounted pawl havingan end portion adapted to be received by the slot to eifect the desiredstopping, the surface of the pawl end opposite the stopping surface whenthe pawl is in stopping position making an angle with a radius of thestop ring through its point of contact therewith such that withdrawal ofthe pawl end from the slot is effected only by a substantial rotationalforce applied to the stop ring, said force being greater than saidfrictional drag but within the torque llimits of said drive.

5. Apparatus of the character claimed in claim e, wherein said slot isradial and the stopping surface of the pawl end comprises an arcconcentric with the axis of pivotal movement Vof the pawl. v

RICHARD XN. MAY,

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS y Dfte Certificate of Correction Patent No.2,536,070 January 2, 1951 RICHARD W. MAY

It is hereby certed that error appears in the printed specification ofthe above numbered patent requiring correction as follows:

Column 1, line 55, for the patent number 2,512,644 read $2,512,664;

and that the said Letters Patent should be read as corrected above, sothat the same may conform to the record of the case in the Patent Oice.

Signed and sealed this 27th day of March, A. D. 1951.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

